Personally, I don't like the arbitrary restriction of once per encounter on skills that seem like basic combat moves like Topple. Unless they also include the option to Shove prone. Spears, Pikes and Glaives should be able to Topple just like Quarterstaff, so perhaps certain weapons should have more uses than one.
Generally, I like the 3.x way of doing things, where you can do Knockdown, Disarm or even Whirlwind attacks as much as you want. They are situational abilities that come with a downside. It's more of a consideration when to use them rather than always doing them once in every encounter. Much more interesting from a tactical point of view.
Fair points. Ignoring trip (everyone should be able to do this), it doesn't really make sense that you can only cleave/charge/bash/pin down a limited number of times.
Perhaps a compromise is that the weapon skills (I still like certain skills being tied to certain weapons: you can't cleave with a rapier or inflict bleeding with a club) have unlimited uses, but they have a negative effect.
-Cleave, Pin Down, and Bash attacks are made at disadvantage. Bash is turned into a "Sunder Armor" reducing the enemy AC by 2 for a turn instead of dealing extra damage
-Charge results in all attacks against you have advantage for a turn
This makes them more situational and interferes less with class skills, as the class skills/feats allow you to do the above things without the negative effect.
